The mental health services literature includes few studies of the causes, and none of the effects, of temporal variation in admissions to PES. This is true despite that PES is among the most expensive of metal health interventions and that PES utilization is often cited as an indicator of the effectiveness of the remainder of the mental health system. Our specific aim is to augment the literature by testing nine hypotheses derived from theory and clinical anecdote. Seven of the hypotheses are concerned with the causes of temporal variation in admissions of adults (i.e., 18 years or older) to psychiatric emergency services. The two remaining hypotheses are concerned with its effects. Data for the tests will be drawn from the public mental health system serving the City and County of San Francisco. The San Francisco public mental health system serves a racially and ethnically diverse population that includes a large number of severely and persistently mentally ill persons (SPM).